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CMPE 150 Fall 2005 Lecture 18

CMPE 150 Fall 2005 Lecture 18. Introduction to Computer Networks. Announcements. Midterm on 11.04. In class, closed books/notes. Homework 3 is up. Due on 11.07.05. Lab this week: discussion/review sessions for midterm. Lab next week: Layer 2. Ethernet. Today. Finish MAC.

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CMPE 150 Fall 2005 Lecture 18

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  1. CMPE 150Fall 2005Lecture 18 Introduction to Computer Networks

  2. Announcements • Midterm on 11.04. • In class, closed books/notes. • Homework 3 is up. • Due on 11.07.05. • Lab this week: discussion/review sessions for midterm. • Lab next week: • Layer 2. • Ethernet.

  3. Today • Finish MAC.

  4. Ethernet Cabling • The most common kinds of Ethernet cabling.

  5. Ethernet Cabling (Cont’d) • Three kinds of Ethernet cabling. • (a) 10Base5, (b) 10Base2, (c) 10Base-T.

  6. Ethernet Topologies • Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.

  7. Switched Ethernet • A simple example of switched Ethernet.

  8. Switched Ethernet (Cont’d) • Point-to-point connections to multi-port hub acting like switch; no collisions. • More efficient under high traffic load: break large shared Ethernet into smaller segments. Switch Hub

  9. Fast Ethernet • IEEE 802.3u • 100Mbps.

  10. Gigabit Ethernet . IEEE 802.11z. . All point to point. • (a) A two-station Ethernet. (b) A multistation Ethernet.

  11. Gigabit Ethernet (Cont’d) • Gigabit Ethernet cabling.

  12. Standardized MACs Topologies Bus Ring Techniques Token bus (802.4) Polling (802.11) Token ring (802.5; FDDI) Round robin Reservation DQDB (802.6) Contention CSMA/CD (802.3) CSMA(802.11)

  13. Wireless LANs

  14. Wireless LANs • 2 modes of operation: • Infrastructure mode. • Ad hoc mode,

  15. Wireless LANs • (a) Wireless networking with a base station. • (b) Ad hoc networking.

  16. IEEE 802.11 • IEEE standard for WLANs. • Standardizes the PHY, MAC, and LLC. • LLC is the same as Ethernet.

  17. The 802.11 Protocol Stack • Part of the 802.11 protocol stack.

  18. IEEE 802.11 Stack (Cont’d) • Distributed access control mechanism (DCF) based on CSMA with optional centralized control (PCF). Contention-free Service (polling) LLC MAC layer PCF Contention Service (CSMA) DCF Physical Layer

  19. 802.11 • Distributed coordination function (DCF) uses CSMA-based protocol (e.g., ad hoc networks). • CD does not make sense in wireless. • Hard for transmitter to distinguish its own transmission from incoming weak signals and noise. • Point coordination function (PCF) uses polling to grant stations their turn to transmit (e.g., cellular networks).

  20. Why a new MAC for wireless?

  21. Why a new MAC for wireless? • The range of a single radio may not cover the entire system.

  22. Why a new MAC for wireless? • (a) The hidden station problem. • (b) The exposed station problem.

  23. 802.11 MAC • DCF: CSMA or CSMA/CA. • PCF; uses polling (centralized round-robin)

  24. What’s CSMA/CA? • CSMA with collision avoidance. • Radios are usually half-duplex. • Cannot send and listen at the same time. • CSMA/CD not possible. • CSMA/CA means both physical- and virtual carrier sensing. • Tries to avoid hidden terminals.

  25. How does CSMA/CA work?

  26. 802.11 Fragments • A fragment burst.

  27. REVIEW

  28. REVIEW (1) • Introduction, overview, terminology. • The Telephone Network (PSTN or POTS). • Addressing. • Data networks. • Communication model. • System components. • Connecting end systems: • Point-to-point (dedicated) link. • Multiple access (shared) link. • Switched point-to-point.

  29. REVIEW (2) • Types of data networks: • Coverage: LAN, MAN, WAN. • Type of connection. • Topology. • Protocols, Layering, Protocol Architecture (Stack), PDUs. • Examples of protocol stacks. • OSI ISO. • TCP/IP. • Protocol stack operation. • Encapsulation/de-encapsulation. • Overhead.

  30. REVIEW (3) • Types of networks: • Circuit-, message-, and packet switching. • Types of network services: • Connection versus connection-less service or datagram versus virtual circuit. • Physical layer (PHY). • Function. • Analog versus digital transmission. • Digitization.

  31. REVIEW (4) • PHY (Cont’d). • Sampling frequency. • Bit rate. • Signals and Systems. • Fourier analysis. • Nyquist’s Theorem. • Shanon’s Theorem. • Bandwidth. • Guided transmission. • More on the PSTN.

  32. REVIEW (5) • PHY (Cont’d). • More on the PSTN. • Components. • Modems. • Modulation. • Baud rate versus bit rate. • Full-, half-, and simplex transmission. • Broadband access: ADSL, Cable, Wireless LL. • Trunking. • Mux’ing and De-mux’ing. • Wireless transmission.

  33. REVIEW (6) • PHY (Cont’d). • Wireless transmission. • Satellite. • Mobile phone system. • DLL. • Functions. • Framing, error-, and flow control. • Framing. • Different framing mechanisms. • Frame fields. • Error control. • Flow control.

  34. REVIEW (7) • DLL. • Error control. • Error detection versus error correction. • Mechanisms for error detection/correction. • Error + Flow control protocols. • Stop-and-Wait. • ARQ. • Sliding window. • Go back N • Selective repeat.

  35. REVIEW (8) • DLL (Cont’d). • Window size and sequence numbers. • Bandwidth-delay product. • Example DLL protocols, • MAC. • Why MACs? • Where is the MAC in the stack? • MACs and LANs. • Multiplexing. • FDM, TDM. Dynamic TDM.

  36. REVIEW (9) • MAC (Cont’d). • Types of MACs. • Contention-based MACs. • Aloha family. • CSMA family, • Ethernet. • Ethernet MAC. • BEB. • Cabling. • Ethernet evolution. • Wireless LANs. • IEEE 802.11.

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